This invention relates generally to fuel nozzles and, more particularly, to methods and apparatus for swirling fuel within fuel nozzles.
Gas turbine engines typically include a plurality of fuel nozzles for supplying fuel to the engine. Improving the life cycle of fuel nozzles installed within the turbine engine extends the longevity of the gas turbine engine. Known fuel nozzles include a delivery system and a support system. Each delivery system delivers fuel to the gas turbine engine and is supported and shielded within the gas turbine engine with the support system. The support system surrounds the delivery system and is thus subjected to higher temperatures than the delivery system which is cooled by the fluid flowing within the fuel nozzle.
Over time, continued exposure to high temperatures produced during gas turbine engine operation may induce thermal stresses on the fuel nozzles and/or facilitate fuel coking within the fuel nozzle. Fuel coking within the nozzle may cause fuel flow reductions and excessive fuel maldistribution within the gas turbine engine, which in-turn may result in turbine inefficiency, turbine component distress,, and reduced engine exhaust gas temperature margin.
To facilitate reducing the effects of the high temperatures, known fuel nozzles include thermal insulation mechanisms, and operate with high fuel flow rates to keep wetted surface temperatures below levels where coking can occur. Known thermal insulation mechanisms include external heat shields, and internal insulating cavities and heat shields which isolate fuel supply tubes from nozzle housing. Such insulation mechanisms add complexity to the fuel nozzle.
To further minimize the effects of high temperatures, during low power operations when high fuel flow rates are not demanded, dribble fuel is supplied to the fuel nozzles. The dribble fuel removes thermal energy from the delivery system that was induced from thermal soak-back of heat stored within the fuel nozzle support system. The additional fuel supplied as dribble fuel to the fuel nozzles may reduce turbine efficiency.
In an exemplary embodiment, gas turbine engine fuel nozzles induce swirling to fuel flowing within the nozzles to facilitate a reduction in fuel coking. Each fuel nozzle includes an inlet, an outlet and a fuel delivery system extending therebetween. The fuel delivery system includes an inner fuel delivery tube and an outer fuel supply tube. The inner fuel supply tube is concentrically aligned within the outer fuel supply tube and includes contoured fuel passageways and a center axis of symmetry.
In use, fuel enters the fuel nozzle inlet and flows towards the contoured fuel passageways. As fuel enters the contoured passageways, the fuel is accelerated locally, and directed angularly with respect to the center axis of symmetry. The contoured passageways impart swirling on the fuel to produce a turbulated fuelflow downstream from the contoured passageways. The turbulated fuelflow facilitates reducing wetted wall temperatures downstream from the contoured passageway, thus lowering operating temperatures of the fuel nozzle. Lowering fuel nozzle operating temperatures facilitates reducing fuel coking within the fuel nozzle, regardless of the fuel flow rate through the fuel nozzle. As a result, the contoured fuel passageways facilitate reducing fuel coking within the gas turbine engine fuel nozzle.